1. Field of the Invention
The present invention relates to a plasma generating apparatus in which a seed plasma is generated by high-frequency discharge and electrons in the seed plasma are used to generate a main plasma by direct-current discharge. This invention further relates to an ion source in which ion beams are extracted from the main plasma generated by the plasma generating apparatus.
Besides being used for an ion source, such a plasma generating apparatus can be utilized as the plasma generating apparatus of a plasma-assisted CVD apparatus, plasma-etching apparatus, etc. The ion source using such a plasma generating apparatus can be utilized, for example, in an ion-doping apparatus (non-mass-separation type ion implanter) for producing liquid crystal display and in an ion-beam apparatus, e.g., an ion implanter for ion implantation into semiconductor substrates, etc.
2. Description of the Related Art
An ion source having an electron-generating chamber and a plasma generating chamber separately disposed from the chamber is disclosed, e.g., in JP-B-7-46586. (The term "JP-B" as used herein means an "examined Japanese patent publication".)
An example of the ion source described in the above reference is shown in FIG. 9. This ion source consists of: an electron-generating chamber 100 in which a plasma is generated upon introduction of a gas (reactive gas) 102 and microwave 104 to form electrons; a plasma-generating chamber 112 connected to the electron-generating chamber 100 through an insulator 108 and an electron extracting electrode 110; and a beam extracting electrode 116 disposed at the opening of the plasma-generating chamber 112. The outer periphery of the electron-generating chamber 100 is surrounded, along the axis thereof, by a cylindrical coil 106 which generates a direct-current magnetic field (satisfying ECR conditions) for plasma confinement. Permanent magnets 114 which form a cusp field have been disposed around the plasma-generating chamber 112.
In this conventional ion source, a plasma is formed in the electron-generating chamber 100, and electrons only are extracted from the plasma into the plasma-generating chamber 112 by means of the electron extracting electrode 110. These electrons are used to cause arc discharge between the electron extracting electrode 110 and the plasma-generating chamber 112, whereby a plasma is formed within the plasma-generating chamber 112. From this plasma, ion beams 118 are extracted by means of the beam extracting electrode 116. The introduction of electrons into the plasma-generating chamber 112 is intended mainly to facilitate the initiation of arc discharge and the formation of a plasma in the plasma-generating chamber 112.
The ion source described above has a drawback that this apparatus as a whole necessarily has a large size because it has the electron-generating chamber 100 separately from the plasma-generating chamber 112.
The conventional ion source has another drawback as follows. In order to obtain ion beams 118 over a large area, the plasma-generating chamber 112 should be enlarged (made to have an increased area) and a highly homogeneous plasma should be formed in this plasma-generating chamber 112. For attaining the high plasma homogeneity, a plurality of electron-generating chambers 100 should be disposed for one plasma-generating chamber 112 to supply electrons dispersedly to the plasma-generating chamber 112 from these charge-generating chambers 100. These electron-generating chambers 100 each should be large in some degree so as to, e.g., decrease plasma loss within the same. However, it is difficult to dispose such large electron-generating chambers 100 for one plasma-generating chamber 112 while preventing the electron-generating chambers 100 from interfering with each other mechanically or magnetically. Consequently, the formation of a plasma or ion beams over a large area is difficult.
In particular, in the case of an ion source which has a cylindrical coil 106 for plasma confinement disposed outside an electron-generating chamber 100, as in the example described above, the ion source has an even larger size due to the cylindrical coil 106. Moreover, the presence of such a cylindrical coil 106 makes it more difficult to dispose a plurality of electron-generating chambers 100 for one plasma-generating chamber 112. In addition, the cylindrical coil 106 necessitates a direct-voltage source for exciting the same, and this results not only in a further increase in the size of the whole apparatus but in an increased cost.